Conventionally, in this kind of exhaust emission purifier of an internal combustion engine, for example as described in Patent Document 1, a predetermined regeneration procedure is executed for recovering exhaust purification catalyst such as NOx storage reduction catalyst arranged in an exhaust system of the internal combustion engine from sulfur poisoning. In the regenerating procedure, the amount of sulfur accumulated in a catalyst is estimated based on an operating state of the engine. If the estimated value of the amount of sulfur is equal to or greater than a predetermined determination value, the regenerating procedure is executed. In the regenerating procedure, the temperature of the catalyst is raised by injecting fuel to the exhaust passage by a fuel adding valve or executing post fuel injection and the exhaust air-fuel ratio is made to be in the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, so that the sulfur is released from the catalyst.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-83298